Partial encoding with padding about data-encoding HOT 3 CLOSED

fn basic_auth(username: &str, password: Option<&str>) -> String {
    let mut buffer = Base64Buf::default();  // This line is new and replaces BASE64.
    let mut output = "Basic ".to_string();
    buffer.encode_append(username.as_bytes(), &mut output);
    buffer.encode_append(b":", &mut output);
    if let Some(password) = password {
        buffer.encode_append(password.as_bytes(), &mut output);
    }
    buffer.finalize(&mut output);  // This line is new.
    output
}

#[derive(Default)]
struct Base64Buf {
    buf: [u8; 4],
}

impl Base64Buf {
    fn encode_append(&mut self, mut input: &[u8], output: &mut String) {
        if self.buf[3] != 0 {
            let len = self.buf[3] as usize;
            let add = std::cmp::min(3 - len, input.len());
            self.buf[len..][..add].copy_from_slice(&input[..add]);
            self.buf[3] += add as u8;
            input = &input[add..];
            if self.buf[3] == 3 {
                BASE64.encode_append(&self.buf[..3], output);
                self.buf[3] = 0;
            }
        }
        let len = input.len() / 3 * 3;
        BASE64.encode_append(&input[..len], output);
        input = &input[len..];
        let len = input.len();
        self.buf[..len].copy_from_slice(input);
        self.buf[3] = len as u8;
    }

    fn finalize(self, output: &mut String) {
        let len = self.buf[3] as usize;
        BASE64.encode_append(&self.buf[..len], output);
    }
}

// Sadly, the following is needed until 3.0.0 is released.
// You may share a single such static in your program.
static BASE64: data_encoding::Encoding = data_encoding::BASE64;

fn basic_auth(username: &str, password: Option<&str>) -> String {
    let mut buf = "Basic ".to_string();
    let mut encoder = BASE64.new_encoder(&mut buf);
    encoder.append(username.as_bytes());
    encoder.append(b":");
    if let Some(password) = password {
        encoder.append(password.as_bytes());
    }
    encoder.finalize();
    buf
}